1. Field of the Invention
The present invention relates to an antenna for a mobile phone, and especially to a multi-band antenna which is suitable for being built in a mobile phone.
2. Description of the Prior Art
Rapid development of wireless communication makes antennas more important in wireless communication products. Particularly, under the tendency of preferring being light, thin and small, the height of an antenna will influence the value of a product, and in most of such antennas, planar antennas and exposed monopole antennas take the main position in designing. The thickness of a conventional dual-band mobile phone is about 7-10 mm; for example, Taiwan patent publication no. 490,884 titled “DUAL-BAND REVERSE F SHAPE PANEL ANTENNA AND RADIATION METAL PLATEREDUCES SIZE OF ANTENNA” discloses a metallic radiation sheet and a systematic grounding surface, and in an example, it is used in a built-in antenna for a mobile phone operated in the mode of dual-band using a mobile communication system GSM (Global System for Mobile Communications) or DCS (Digital Cellular System), it makes evidently thicker of the entire mobile phone over 10 mm. If we apply the above stated technique of the conventional antenna to a thin mobile phone, will shall encounter a problem of overly large thickness of the antenna, thus the requirement for thinning mobile phones will not be really satisfied.
In order to solve this problem, manufacturers in the art most adopt monopole antennas in designing, by virtue that an exposed monopole antenna that protruding out of the grounding surface is less influenced by the grounding surface, hence the thickness of the antenna can be reduced to meet the requirement in application of the thin mobile phones.
However, no matter which of a planar antenna or a monopole antenna it is, by the fact that the applicable design space in the antenna is limited, for a GSM, its band generally can only exactly include the operation band of GSM 850; while mobile phones used in the present days have been developed toward the tendency of multi-band, most of the conventional inverted F-type antennas or monopole antennas can only meet the dual-band requirement of GSM/DCS within their limited spaces, its is hard to design an antenna meeting the requirement of multi-band for application.